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  • 1.
    Evans, Simon R.
    et al.
    Univ Oxford, Dept Zool, Edward Grey Inst, Oxford OX1 3PS, England..
    Sheldon, Ben C.
    Univ Oxford, Dept Zool, Edward Grey Inst, Oxford OX1 3PS, England..
    Quantitative Genetics of a Carotenoid-Based Color: Heritability and Persistent Natal Environmental Effects in the Great Tit2012In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 179, no 1, p. 79-94Article in journal (Refereed)
    Abstract [en]

    The information content of signals such as animal coloration depends on the extent to which variation reflects underlying biological processes. Although animal coloration has received considerable attention, little work has addressed the quantitative genetics of color variation in natural populations. We investigated the quantitative genetics of a carotenoid-based color patch, the ventral plumage of mature great tits (Parus major), in a wild population. Carotenoid-based colors are often suggested to reflect environmental variation in carotenoid availability, but numerous mechanisms could also lead to genetic variation in coloration. Analyses of individuals of known origin showed that, although plumage chromaticity (i.e., color) was moderately heritable, there was no significant heritability to achromaticity (i.e., brightness). We detected multiple long-lasting effects of natal environment, with hatching date and brood size both negatively related to plumage chromaticity at maturity. Our reflectance measures contrasted in their spatiotemporal sensitivity, with plumage chromaticity exhibiting significant spatial variation and achromatic variation exhibiting marked annual variation. Hence, color variation in this species reflects both genetic and environmental influences on different scales. Our analyses demonstrate the context dependence of components of color variation and suggest that color patches may convey multiple aspects of individual state.

  • 2.
    Evans, Simon R.
    et al.
    Univ Oxford, Dept Zool, Edward Grey Inst, Oxford OX1 2JD, England..
    Summers, Alex G. R.
    Univ Oxford, Dept Zool, Edward Grey Inst, Oxford OX1 2JD, England..
    Sheldon, Ben C.
    Univ Oxford, Dept Zool, Edward Grey Inst, Oxford OX1 2JD, England..
    Seasonality of carotenoid-based plumage coloration: modelling wavelength-specific change through spectral reconstruction2012In: Journal of Avian Biology, ISSN 0908-8857, E-ISSN 1600-048X, Vol. 43, no 3, p. 234-243Article in journal (Refereed)
    Abstract [en]

    Plumage coloration has provided important model systems for research on signal expression. Whilst it had previously been assumed that moulting provided the only mechanism to change plumage coloration, recent studies have shown plumage colours to be seasonally dynamic, with implications both for the quantification of expression and for any signalling role. However, the mechanistic processes underlying such change remain uncertain. Here, we describe within-moult shifts in expression of a carotenoid-based colour trait the yellow ventral plumage of the great tit Parus major over a nine-month timespan. We report that plumage chromaticity (colour) but not achromaticity (brightness) exhibits a marked seasonal decline, independent of sex, age or body condition, and at a constant rate across twelve environmentally heterogeneous plots within our study site. To gain a greater understanding of the mechanisms underlying this change we employed a spectral reconstruction approach, that generates predicted spectra for any timepoint within the sampling period. By comparing spectra for both early and late in the moult we show that the seasonal decline in chromaticity is driven by both a marked reduction in ultraviolet (UV) reflectance and, to a lesser extent, loss of active carotenoid pigments. Thus, our study shows that seasonal loss of chromaticity in the great tit is driven by altered reflectance primarily in the UV section of the spectrum, a finding made possible by the use of spectral compartmentalisation and multi-parallel modelling to produce reconstructed spectra. Whether change in plumage coloration influences signal function will depend on the dynamics of the signalling system but it could clearly inflate patterns such as assortative mating and should be considered in studies of colour expression.

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